1. Field of Invention
The invention relates to a method for signal detection and obtaining, and more particularly to a method to obtain a tracking error signal of an optical storage medium.
2. Related Art
The positions of tracks are determined by the phase difference of signals detected by photo detectors. Regarding the high-density optical record medium, in U.S. Pat. No. 6,137,755 (Deriving a tracking error signal from a time difference between detector signals) discloses a circuit for obtaining the tracking error signal in order to increase the reliability of the signal.
The circuitry is shown in FIG. 1. A first summing signal F1 is input into a slicer 12 via a capacitor 11, the input terminal of which couples a resistor 13 to a ground to generate a suitable slicing voltage level. The signal S1 from the slicer 32 is input to the first input of a logic comparator (EXOR) 14, which produces a comparing signal A. After a lowpass filer including a resistor 15 and a capacitor 16 deals with the comparing signal A, the signal A is then input to a negative terminal of a difference amplifier 18 via a resistor 17. The signal from the difference amplifier 18 is the tracking error signal TE. Similarly, a second summing signal F2 is input to the positive terminal of the difference amplifier 39 via a capacitor 21, a slicer 22, a resistor 23, a logic comparator 24, a lowpass filter including a resistor 25 and a capacitor 26, and a resistor 27. The positive terminal of the difference amplifier 18 couples a resistor 28 to the ground. The circuit further comprises a delayer 20 to obtain a delay signal S1d, which is input to the second input of the logic comparator 14 and the logic comparator 24 respectively.
Using the first summing D1 to obtain the delay signal S1d, which is used to acquire the phase error, creates a problem. The frequency at which the delay signal S1d is acquired is cause for concern. As shown in FIG. 2, when the delay signal S1d is too small or too large, the range of the delay signal S1d is between Tp and 3T-Tp.
The pulse width of the signal for detecting the phase difference becomes wider if the delay signal S1d is larger. The phase-comparing circuit is easily implemented in this situation. If the delay is 3T-Tp, the pulse width from the phase comparator is 3T-2Tp. If the increasing frequency is caused by high-density data or high accessing speed, handling the frequency of the signal becomes difficult.
The method employs only one signal to obtain the delay signal, which is used to detect the lead and the lag of the signals. Thus, the method disclosed in U.S. Pat. No. 6,137,755 needs improvement because the reliability of the delay range is lower.